Heat transfer device with nested layers of helical fluid channels

ABSTRACT

Systems, apparatuses, and methods relating to heat transfer devices having nested layers of helical fluid channels. In some examples, a device for transferring heat includes a set of nested tubular walls and a plurality of helical walls intersecting each of the nested tubular walls to form one or more first channel layers nested with one or more second channel layers. Each of the first and second channel layers includes a plurality of helical fluid channels. A first intake and a first outtake are in fluid communication with one another via the plurality of helical fluid channels of each first channel layer, for flow of a first fluid through the device. A second intake and a second outtake are in fluid communication with one another via the plurality of helical fluid channels of each second channel layer, for flow of a second fluid through the device.

BACKGROUND

A heat exchanger is a device for transferring heat between a pair offluids, often without contact of the fluids with one another. Heatexchangers are used in a wide variety of heating and coolingapplications and have three basic configurations for travel of the pairof fluids: parallel flow (in the same direction), cross flow, andcounterflow (in opposite directions). Of these configurations,counterflow heat exchangers can transfer heat most efficiently. However,traditional counterflow heat exchangers may be unable to achieve thehigh efficiency of heat transfer and the compactness needed in demandingapplications, such as power generation, that require operation at hightemperatures and pressures. Moreover, these traditional heat exchangerscan be bulky and heavy due to complex fluid manifolds and thusunsuitable where minimizing size and weight are very important, such ason an aircraft. A new counterflow heat exchanger is needed.

SUMMARY

The present disclosure provides systems, apparatuses, and methodsrelating to heat transfer devices (heat exchangers) having nested layersof helical fluid channels for directing fluid flow. In some examples, adevice for transferring heat between a first fluid and a second fluidincludes a set of nested tubular walls and a plurality of helical wallsintersecting each of the nested tubular walls to form one or more firstchannel layers nested with one or more second channel layers. Each ofthe one or more first channel layers and the one or more second channellayers includes a plurality of helical fluid channels. A first intakeand a first outtake are in fluid communication with one another via theplurality of helical fluid channels of each first channel layer, forflow of the first fluid through the device from the first intake to thefirst outtake. A second intake and a second outtake are in fluidcommunication with one another via the plurality of helical fluidchannels of each second channel layer, for flow of the second fluidthrough the device from the second intake to the second outtake.

In some examples, an aerospace vehicle (interchangeably called a flightvehicle) includes a vehicle body, an engine connected to the vehiclebody and configured to power the vehicle body in a flight mode, and aheat transfer device connected to the vehicle body and/or the engine.The heat transfer device includes a set of nested tubular walls, aplurality of helical walls intersecting each of the nested tubular wallsto form one or more first channel layers nested with one or more secondchannel layers. Each of the one or more first channel layers and the oneor more second channel layers includes a plurality of helical fluidchannels. A first intake and a first outtake are in fluid communicationwith one another via the helical fluid channels of each first channellayer, for flow of a first fluid through the heat transfer device fromthe first intake to the first outtake. A second intake and a secondouttake are in fluid communication with one another via the plurality ofhelical fluid channels of each second channel layer, for flow of asecond fluid through the heat transfer device from the second intake tothe second outtake.

In some examples, a method of transferring heat between fluids uses aheat transfer device including a set of nested tubular walls intersectedby a plurality of helical walls to form one or more first channel layersnested with one or more second channel layers. In the method, a firstfluid is passed through the heat transfer device between a first intakeand a first outtake via a plurality of helical fluid channels of eachfirst channel layer of the heat transfer device. A second fluid ispassed through the heat transfer device between a second intake and asecond outtake via a plurality of helical fluid channels of each secondchannel layer of the heat transfer device.

Features, functions, and advantages may be achieved independently invarious examples of the present disclosure, or may be combined in yetother examples, further details of which can be seen with reference tothe following description and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of an illustrative counterflow heat transferdevice having nested layers of helical fluid channels, in accordancewith aspects of the present disclosure.

FIG. 2 is another schematic cross-sectional view of the heat transferdevice of FIG. 1 , taken along line 2-2 of FIG. 1 orthogonal to acentral axis of the device.

FIG. 3 is an isometric view of another illustrative counterflow heattransfer device having nested layers of helical fluid channels.

FIG. 4 is a top view of the heat transfer device of FIG. 3 .

FIG. 5 is a side view of the heat transfer device of FIG. 3 .

FIG. 6 is an end view of the heat transfer device of FIG. 3 , takenalong line 6-6 of FIG. 5 and showing a hot outtake and a cold intake ofthe heat transfer device.

FIG. 7 is an opposite end view of the heat transfer device of FIG. 3 ,taken along line 7-7 of FIG. 5 and showing a hot intake and a coldouttake of the heat transfer device.

FIG. 8 is a cutaway view of the heat transfer device of FIG. 3 , withflow paths for hot and cold fluids indicated using arrows havingdifferent line weights.

FIG. 9 is a sectional view of the heat transfer device of FIG. 3 , takenalong line 9-9 of FIG. 5 .

FIG. 10 is a sectional view of the heat transfer device of FIG. 3 ,taken along line 10-10 of FIG. 4 .

FIG. 11 is a fragmentary sectional view of the heat transfer device ofFIG. 3 , taken around the region indicated in FIG. 9 .

FIG. 12 is a cross-sectional view of the heat transfer device of FIG. 3, taken along line 12-12 of FIG. 5 through a central section of the heattransfer device.

FIG. 13 is a cross-sectional view of the heat transfer device of FIG. 3, taken generally along line 13-13 of FIG. 5 through a pair of manifoldslocated near one end of the heat transfer device.

FIG. 14 is another cross-sectional view of the heat transfer device ofFIG. 3 , taken generally along line 14-14 of FIG. 5 through another pairof manifolds located near the opposite end of the heat transfer device.

FIG. 15 is a fragmentary sectional view of an illustrative heat transferdevice having the same basic structure as the heat transfer device ofFIG. 3 , viewed generally as in FIG. 11 , and showing pairs of alignedprotrusions projecting into the lumens of pairs of axially-adjacenthelical fluid channels from each helical wall of a plurality of helicalwalls.

FIG. 16 is a fragmentary sectional view of another illustrative heattransfer device having the same basic structure as the heat transferdevice of FIG. 3 , viewed generally as in FIG. 11 , and showing pairs ofprotrusions projecting into the lumens of pairs of axially-adjacenthelical fluid channels from each helical wall of a plurality of helicalwalls.

FIG. 17 is a fragmentary sectional view of still another illustrativeheat transfer device having the same basic structure as the heattransfer device of FIG. 3 , viewed generally as in FIG. 11 , and showingprotrusions projecting into the lumens of helical fluid channels from aset of nested tubular walls.

FIG. 18 is a fragmentary sectional view of yet another illustrative heattransfer device having the same basic structure as the heat transferdevice of FIG. 3 , viewed generally as in FIG. 11 , and showing openingsformed in a helical wall and allowing fluid communication betweenadjacent helical fluid channels, intermediate the ends thereof, withineach channel layer.

FIG. 19 is a schematic diagram of an illustrative aerospace vehicleincorporating the heat transfer device of FIG. 1 in a thermodynamiccycle that converts heat to another form of energy.

FIG. 20 is a schematic diagram of an illustrative power plantincorporating the heat transfer device of FIG. 1 in a thermodynamiccycle that converts heat to another form of energy.

FIG. 21 is a flowchart depicting steps of an illustrative method oftransferring heat between a pair of fluids using a heat transfer deviceof the present disclosure.

FIG. 22 is a schematic diagram of an illustrative aircraft.

FIG. 23 is a flowchart depicting steps of an illustrative aircraftmanufacturing and service method.

DETAILED DESCRIPTION

Various aspects and examples of a heat transfer device having nestedlayers of helical fluid channels, as well as related methods, aredescribed below and illustrated in the associated drawings. Unlessotherwise specified, a heat transfer device in accordance with thepresent teachings, and/or its various components may, but is notrequired to, contain at least one of the structures, components,functionalities, and/or variations described, illustrated, and/orincorporated herein. Furthermore, unless specifically excluded, theprocess steps, structures, components, functionalities, and/orvariations described, illustrated, and/or incorporated herein inconnection with the present teachings may be included in other similardevices and methods, including being interchangeable between disclosedexamples. The following description of various examples is merelyillustrative in nature and is in no way intended to limit thedisclosure, its application, or uses. Additionally, the advantagesprovided by the examples described below are illustrative in nature andnot all examples provide the same advantages or the same degree ofadvantages.

This Detailed Description includes the following sections, which followimmediately below: (1) Overview; (2) Examples, Components, andAlternatives; (3) Illustrative Combinations and Additional Examples; (4)Advantages, Features, and Benefits; and (5) Conclusion. The Examples,Components, and Alternatives section is further divided into subsectionsA through H, each of which is labeled accordingly.

Overview

In general, a heat transfer device in accordance with the presentteachings includes a thermally conductive structure having a first flowpath for a first fluid and a second flow path for a second fluid, wherethe structure is configured to conduct heat between the first fluid andthe second fluid. The first and second flow paths may be concentricwith, and isolated from, one another. The heat transfer device may be asingle additively manufactured unit and may also be referred to as aheat exchanger, a heat sink, and/or a cooler. Although the heat transferdevice may be used in any suitable heat transfer application, in someexamples, the device may be particularly useful for hightemperature/high pressure applications, such as in a thermodynamic cycleto generate power from heat. Accordingly, within examples, the heattransfer device may have particular utility for thermal management in ahigh speed aircraft (e.g., a hypersonic air vehicle, such as ahypersonic airplane or a missile) or a power plant (e.g., a concentratedsolar power plant or nuclear power plant).

The first flow path includes one or more first channel layers and thesecond flow path includes one or more second channel layers. Each of thefirst and second channel layers encircles a central axis of the heattransfer device in a spaced relation to the central axis (i.e., withoutintersecting the central axis). The first and second channel layers mayform a nested set of channel layers, may be concentric with one another,and/or may be located radially inward or radially outward of each otherfirst/second channel layer, such as to form an alternating radial seriesof first and second channel layers. Each first channel layer includes aplurality of first helical fluid channels, and each second channel layerincludes a plurality of second helical fluid channels. The first orsecond helical fluid channels of each first channel layer or each secondchannel layer are rotationally offset from one another about the centralaxis. The first flow path and the second flow path are not in fluidcommunication with one another. More specifically, the first channellayers and first helical fluid channels thereof are not in fluidcommunication with the second channel layers and second helical fluidchannels thereof within the heat transfer device.

The first and second channel layers, and the first and second helicalfluid channels thereof, are formed by a set of nested tubular wallsintersected by a plurality of helical walls. The nested tubular wallsmay be concentric with another and each centered on the central axis ofthe heat transfer device. Each channel layer is located between anadjacent pair of the nested tubular walls or, in some examples, one ofthe channel layers is located inside the innermost tubular wall of theset of nested tubular walls. The plurality of helical walls may becoaxial with the set of nested tubular walls. Each helical wall spans aspace (a gap) between each adjacent pair of the nested tubular walls,and collectively the helical walls divide the space into a plurality offirst or second helical fluid channels. Each first helical fluid channelof at least one first channel layer and each second helical fluidchannel of at least one second channel layer is bounded by an adjacentpair of the nested tubular walls and by an adjacent pair of the helicalwalls. Within examples, the use of nested tubular walls intersected byhelical walls may allow the heat transfer device to have a larger wettedsurface area for more efficient heat transfer, a more robust geometry towithstand large pressure differentials and/or high temperatures, asmaller size, a reduced weight, and/or a reduced pressure drop for fluidflow.

Examples, Components, and Alternatives

The following sections describe selected aspects of exemplary heattransfer devices as well as related systems and/or methods. The examplesin these sections are intended for illustration and should not beinterpreted as limiting the entire scope of the present disclosure.Terms such as “upper”, “lower”, “left”, and “right” may be used to inthe context of the drawings to refer to relative positions of thedescribed components, but it should be understood that any of thedescribed components or heat transfer devices may be used in anyorientation. Each section may include one or more distinct examples,and/or contextual or related information, function, and/or structure.

A. Illustrative Counterflow Heat Transfer Device

This subsection describes an illustrative heat transfer device 100having concentric channel layers of helical fluid channels; see FIGS. 1and 2 .

FIG. 1 shows a schematic diagram of an illustrative heat transfer device100 (interchangeably called a heat exchanger). The heat transfer deviceprovides a first flow path 102 and a second flow path 104 for flow of afirst fluid 106 and a second fluid 108, respectively, through the devicewithout contact of the fluids with one another. In FIGS. 1 and 2 , firstfluid 106 is represented by smaller dots and second fluid 108 by largerdots.

Each flow path 102, 104 includes an intake, an outtake, and helicalfluid channels located along the flow path intermediate the intake andthe outtake. (Each intake interchangeably is described as an inlet, andeach outtake interchangeably is described as an outlet.) First flow path102 has a first intake 110 and a first outtake 112 that are in fluidcommunication with one another via each of a plurality of first helicalfluid channels 114. Similarly, second flow path 104 has a second intake116 and a second outtake 118 that in fluid communication with oneanother via each of a plurality of second helical fluid channels 120.First helical fluid channels 114 and second helical fluid channels 120are formed by a central section 121, which is located between a pair ofopposite end sections 122 a, 122 b. Each of the first and second flowpaths is described as a helical path because each is composed of helicalfluid channels along a majority of its length. The first and second flowpaths are concentric (and coaxial) with one another, as determined bythe helical portion of each path.

When first fluid 106 and second fluid 108 enter heat transfer device 100at first and second intakes 110, 116, respectively, the two fluids havedifferent temperatures. For example, first fluid 106 may be hotter thansecond fluid 108 (or vice versa). Accordingly, first fluid 106 may bedescribed in relative terms as a hot fluid and second fluid 108 as acold fluid (or vice versa). As the two fluids travel through heattransfer device 100 on first flow path 102 and second flow path 104,heat is transferred from first fluid 106 to second fluid 108, such thatfirst fluid 106 leaves first outtake 112 cooled and second fluid 108leaves second outtake 118 heated.

First and second flow paths 102, 104 are arranged to permit counterflowof first and second fluids 106, 108 through heat transfer device 100. Inother words, the first and second fluids can travel in oppositedirections through the heat transfer device on generally parallel paths.As indicated by arrows extending through the first and second intakes110, 116 and the first and second outtakes 112, 118, first fluid 106flows from left to right in FIG. 1 through heat transfer device 100 fromend section 122 a to end section 122 b, while second fluid 108 flowsfrom right to left, from end section 122 b to end section 122 a.

Each flow path 102, 104 also includes a pair of manifolds to connect theintake and outtake of the flow path to the corresponding first or secondhelical fluid channels. More specifically, first flow path 102 has afirst inflow manifold 123 intermediate first intake 110 and firsthelical fluid channels 114. The first flow path also has a first outflowmanifold 124 intermediate first helical fluid channels 114 and firstouttake 112. First inflow manifold 123 allows first flow path 102 tobranch as it extends from first intake 110 to first helical fluidchannels 114, and first outflow manifold 124 allows branches of firstflow path 102 to merge as the path extends from first helical fluidchannels 114 to first outtake 112. Similarly, second flow path 104 has asecond inflow manifold 126 intermediate second intake 116 and secondhelical fluid channels 120. The second flow path also has a secondoutflow manifold 128 intermediate second helical fluid channels 120 andsecond outtake 118. Second inflow manifold 126 allows second flow path104 to branch as it extends from second intake 116 to second helicalfluid channels 120, and second outflow manifold 128 allows branches ofsecond flow path 104 to merge as the path extends from second helicalfluid channels 120 to second outtake 118.

The helical fluid channels of each flow path 102, 104 are arranged inmultiple channel layers, each including a plurality of helical fluidchannels (within examples, at least 3, 4, 5, 6, 8, or 10 helical fluidchannels, among others). In heat transfer device 100, a plurality offirst helical fluid channels 114 are located in each of first channellayers 130 a, 130 b, and 130 c, and a plurality of second helical fluidchannels 120 are located in each of second channel layers 132 a, 132 b,and 132 c. The channel layers are nested and concentric with oneanother. A portion of first channel layer 130 b is magnified on theright side of FIG. 1 to show the presence of five helical fluid channels114, although within examples, more or fewer helical fluid channels maybe present in the channel layer. Within examples, the number of helicalfluid channels per channel layer, and the size of each helical fluidchannel, may be selected to achieve a desired balance between theefficiency of heat transfer and the pressure drop.

The number of channel layers present in the device may be chosen basedon the heat transfer rate and efficiency needed. Increasing the numberof channel layers increases the wetted surface area, which can increasethe heat transfer rate, the heat transfer efficiency, or both, at theexpense of increased size, weight, and/or pressure drop. For practicalreasons, there may be at least a minimum spacing, such as at least aboutone millimeter, between opposite channel walls of the helical fluidchannels (e.g., the size of the gap between adjacent tubular walls ofthe nested tubular walls), to avoid excessive pressure drops. The sizeof the device also or alternatively may be chosen to meet theperformance requirements of a particular application. For example, thedevice may be enlarged in length and/or diameter to provide a higherheat transfer capacity.

First and second fluids 106, 108 may be supplied to first and secondintakes 110, 116 by separate fluid systems, each including a pump orother compressor and a fluid source. The fluids may include, but are notlimited to, gases such as nitrogen or atmospheric air, a substance in asupercritical state, such as supercritical carbon dioxide, steam,dielectric liquid coolants such as silicone oils, non-dielectric liquidcoolants such as aqueous solutions of ethylene glycol, and/or newercoolants such as nanofluids or ionic liquids, among others. For example,first fluid 106 may be air or steam and second fluid 108 may besupercritical carbon dioxide. In some examples, the cold fluid is aworking fluid in a power cycle that converts heat to another form ofenergy. The first and second fluids are at different temperatures whenthey enter the heat transfer device, and may have different chemicalcompositions from one another or the same chemical composition.

FIG. 2 shows a less schematic cross-sectional view of heat transferdevice 100 taken through channel layers 130 a-130 c and 132 a-132 c ofcentral section 121, orthogonal to a central axis 134 of the device.Channel layers 130 a-130 c for first fluid 106 are arranged to alternatewith channel layers 132 a-132 c for second fluid 108, in a radialdirection 136, that is, along a radius that intersects, and is orientedorthogonal to, central axis 134.

Heat transfer device 100 has a set of nested tubular walls 138 a-138 feach encircling and centered on central axis 134, and thus concentricwith one another. Six nested tubular walls are shown here, but in otherexamples, the heat transfer device may have any suitable number ofnested tubular walls, such as at least three, four, five, or more. Thenumber of nested tubular walls in the set may be determined by the sizeof the heat transfer device and the rate of heat transfer required, witha larger heat transfer device and/or a higher rate of transfer generallyutilizing a greater number of nested tubular walls. The set of nestedtubular walls includes an outermost tubular wall 138 f, an innermosttubular wall 138 a located at least predominantly inside outermosttubular wall 138 f, and tubular walls 138 b-138 e each located betweenthe outermost and innermost tubular walls and at least predominantlyinside the outermost tubular wall. In the example depicted, each of thetubular walls is cylindrical and of successively larger diameter whenconsidered in order from innermost to outermost. In other examples, thetubular walls are non-cylindrical, such as having a tubular geometrybased on an oval, wavy, or irregular cross-sectional shape. Tubularwalls 138 a-138 f are spaced from one another in radial direction 136.Within examples, the spacing of the tubular walls from one another maybe uniform or may vary. Varying the spacing may facilitate adjustment(e.g., equalization) of the wetted surface area of the first channellayers relative to the second channel layers and/or may accommodate therespective viscosities of the first and second fluids (e.g., a largerradial gap between adjacent tubular walls for a more viscous fluid and asmaller radial gap for a less viscous fluid). Within examples, thethickness of tubular walls 138 a-138 f may be uniform or varying foreach tubular wall, and uniform or varying among the tubular walls. Aconstant thickness for a given tubular wall may be advantageous to avoidpoints of weakness, and a varying thickness for the tubular wall may bedesired to make the tubular wall thicker at positions where stress isexpected to be greater, such as at junctions with other walls. A varyingthickness among the tubular walls may be advantageous to strengthen theheat transfer device against external/internal pressure differentials.For example, outermost tubular wall 138 f may function as ahousing/shell for the device, and thus may be thicker than the othertubular walls to protect the heat transfer device from the pressuredifferential between inside and outside the heat transfer device.

Heat transfer device 100 has a plurality of helical walls 140 eachintersecting each nested tubular wall of the set of nested tubular walls138 a-138 f, to form first helical fluid channels 114 of first channellayers 130 a-130 c and second helical fluid channels 120 of secondchannel layers 132 a-132 c. In the example depicted, the heat transferdevice has five helical walls 140 each intersecting each of nestedtubular walls 138 a-138 f, to form five helical fluid channels 114 orfive helical fluid channels 120 in each first or second channel layer.However, within examples, more or fewer helical walls may be present,such as at least two, three, four, five, six, eight, or ten, amongothers, to form a matching number of helical fluid channels in eachchannel layer. Helical walls 140 are coaxial with the set of nestedtubular walls 138 a-138 f and thus centered on central axis 134.

Each helical wall 140 of the plurality of helical walls extends radiallyoutward, linearly, in a different radial direction 136, at a givenposition along central axis 134. The helical wall intersects each ofnested tubular walls 138 a-138 f. Accordingly, the helical wall extends(at least) from innermost tubular wall 138 a, which is closest tocentral axis 134, to outermost tubular wall 138 f, which is farthestfrom central axis 134. In the depicted example, the helical wall alsoprotrudes radially inward from the innermost tubular wall into a lumen142 thereof, to form a helical rib 144 having a free edge in lumen 142.In other examples, helical ribs 144 join one another at central axis134. In other examples, helical walls 140 do not protrude into lumen142.

Helical walls 140 match one another in size and shape. The helical wallshave the same helical lead and the same radius as one another. They arerotationally offset from one another about central axis 134, optionallyuniformly offset from one another by the same angle of rotation, suchthat the helical pitch of the helical walls is uniform. A uniformrotational offset among helical walls 140 may be desirable to producethe same size of helical fluid channels within a given channel layer andthe same resistance to flow among the helical fluid channels of thechannel layer. The term “helical pitch,” as used herein, is the distancebetween adjacent helical walls measured parallel to the central axis atthe periphery of the helical walls. The “helical lead,” as used herein,is the axial distance spanned by one complete turn of a helical wall,measured parallel to the central axis at the periphery of the helicalwall.

Helical walls 140 and nested tubular walls 138 a-138 f collectivelybound helical fluid channels 114, 120. The helical walls 140 divide aspace 146 (a gap) between each adjacent pair of tubular walls 138 a-138f, and at least a radially outer portion of lumen 142 of innermosttubular wall 138 a, into two or more helical fluid channels 114 or twoor more helical fluid channels 120. More specifically, each adjacentpair of the helical walls provides a series of pairs ofrotationally-offset channel walls 148 each partially bounding one of thehelical fluid channels of a helical column of helical fluid channels114, 120. Similarly, each adjacent pair of nested tubular walls 138a-138 f provides a circumferential series of pairs of radially-spacedchannel walls 150 each partially bounding one of the helical fluidchannels of a circumferential row of helical fluid channels 114 or 120.Helical fluid channels 120 of core channel layer 132 a are formed insideinnermost tubular wall 138 a. These helical fluid channels may be openhelical passages 152 that are open along a radially inward side of eachchannel, and thus in fluid communication with one another along eachhelical passage, intermediate the ends thereof.

Within examples, helical walls 140 may have three primary functions.First, the helical walls, also called helical fins or heat transferwalls, provide wetted heat transfer surfaces that increase theefficiency of heat transfer. Second, the helical walls conduct heatbetween adjacent channel layers, which also increases the efficiency ofheat transfer. Third, the helical walls may be radially continuous,extending from the outermost tubular wall to the innermost tubular wall,which may create a direct, continuous load path from the exterior wallof the heat transfer device to the innermost tubular wall. This loadpath allows the helical walls to handle high pressure differentials intension. Each helical wall may have a uniform thickness, or may decreasein thickness (e.g., may taper or thin stepwise) toward the central axisof the device, to fine-tune strength capability and potentially reduceweight.

Heat transfer device 100 is composed of a thermally conductive material,which may be metallic, polymer, or polymer composite (e.g., carbon fiberreinforced polymer (CFRP)), among others. The heat transfer device maybe constructed by additive manufacturing, such as from a powder orfilament of the thermally conductive material. If formed of polymer orpolymer composite, the device being constructed may be treated by apost-build sealing process to ensure pressure containment (e.g., byepoxy vacuum infiltration). The heat transfer device may includemultiple materials, or may be produced from a single material. Thermalconductivity, specific heat, density, and phase transition temperatures,along with other factors, may be considered in selecting a material orcombination of materials. Appropriate or desirable materials may dependon an intended application and a selected additive manufacturing method.

Heat transfer device 100 is partially or entirely unitary. In someexamples, the nested tubular walls and helical walls are formedcollectively as a single monolithic structure. In some examples, thesingle monolithic structure includes each manifold and/or each intakeand outtake. The heat transfer device may be additively manufactured inone process, without need for assembly of separate parts.

Heat transfer device 100 may have improved reliability, as a result ofunitary construction. Less than optimal performance of the heat transferdevice related to issues with connection or interaction of parts may beeliminated. Part count, production time, and manufacturing costs may bereduced. Unitary construction may also improve heat transfer betweenfluids 106, 108 by removing joints and interfaces and increasing thewetted surface area of the heat transfer device, and creating flow pathsthat are difficult or impossible to construct without the benefit ofadditive manufacturing.

B. Illustrative Counterflow Heat Transfer Device

This subsection describes another illustrative heat transfer device 200having concentric layers of helical fluid channels; see FIGS. 3-14 . Therelative terms “hot” and “cold” are used as arbitrary, interchangeabledesignations in this subsection to distinguish respective structuresthat contact a pair of fluids of different temperature.

Heat transfer device includes a hot flow path 202 (dashed arrows) forflow of a hot fluid 206 through the device, and a cold flow path 204(solid arrows) for flow of a cold fluid 208 through the device, wherethe two paths are completely separate from one another (see FIGS. 8 and12-14 ). Both paths are created by a central section 221 and a pair ofend sections 222 a, 222 b, which are formed collectively by additivemanufacturing as a single monolithic unit (see FIGS. 3-5 and 9 ).Central section 221 is cylindrical and each end section 222 a, 222 btapers away from central section 221 to a pair of cylindrical ports (anintake and an outtake) of substantially smaller diameter than thecentral section.

The cylindrical ports are a hot outtake 212 and a cold intake 216 forend section 222 a, and a hot intake 210 and a cold outtake 218 for endsection 222 b (see FIGS. 3-9 ). (The intakes and outtakes areinterchangeably called inlets and outlets, respectively.) Heat transferdevice 200 defines a longitudinal axis 234 (see FIGS. 4 and 5 ). Hotintake 210, hot outtake 212, cold intake 216, and cold outtake 218define respective axes 254 that are parallel to one another andlongitudinal axis 234, and coplanar with one another (see FIG. 4 ). Thisaxial arrangement of intakes and outtakes avoids sharp turns and thusthe pressure drop associated with such sharp turns. The intakes andouttakes may have different sizes and/or features to ensure that theseports are distinguishable from one another for proper connection tofluid sources.

Hot intake 210 and cold intake 216 each include a swirl initiator 256(see FIGS. 3, 6, and 7 ). The swirl initiator includes one or moreflow-steering vanes 258 projecting into the lumen of the correspondingintake (see FIGS. 3 and 6-9 ), and promotes a swirling flow 260 of a hotor cold fluid passing through the intake (see FIG. 8 ). Eachflow-steering vane 258 may be helical. The swirling flow advantageouslyencourages mixing of each fluid within heat transfer device 200, andthus drives more rapid and efficient heat transfer between the pair offluids 206, 208 flowing through the device. In addition, the swirlingflow provides better alignment of fluid flow with the inlets of thehelical fluid channels. This better alignment of fluid flow avoids theneed for an abrupt turn in flow direction, which may result in anundesirably large pressure drop and flow maldistribution, when eachfluid enters the helical fluid channels.

FIG. 9 shows a sectional view of heat transfer device 200. Each endsection 222 a, 222 b includes a pair of manifolds each providing fluidcommunication between a port and hot helical fluid channels 214 or coldhelical fluid channels 220 of central section 221. More specifically,end section 222 a has a cold inflow manifold 226 that connects coldintake 216 to cold helical fluid channels 220, and also has a hotoutflow manifold 224 that connects hot helical fluid channels 214 to hotouttake 212. Similarly, end section 222 b has a hot inflow manifold 223that connects hot intake 210 to hot helical fluid channels 214, and alsohas a cold outflow manifold 228 that connects cold helical fluidchannels 220 to cold outtake 218. The structure of these manifolds isexplained in more detail below.

Central section 221 of the depicted example includes six nested tubularwalls 238 a-238 f and twelve helical walls 240 arranged coaxially withone another (see FIGS. 9-12 ). Within examples, the number of nestedtubular walls may be at least three, four, five, six, eight, or ten,among others. Within examples, the number of helical walls may be atleast two, three, four, five, six, eight, or ten, among others. In thedepicted example, the nested tubular walls are intersected by thehelical walls to form six concentric channel layers, namely, three hotchannel layers 230 a-230 c and three cold channel layers 232 a-232 carranged alternately. In other words, from innermost to outermost alongradial direction 236, the order of channel layers is cold channel layer232 a, hot channel layer 230 a, cold channel layer 232 b, hot channellayer 230 b, cold channel layer 232 c, and hot channel layer 230 c.Within examples, the heat transfer device may have at least one, two,three, four, five, or more hot channel layers, at least one, two, three,four, five, or more cold channel layers, and at least two, three, four,five, six, eight, or ten channel layers (each hot or cold). Each of thehot channel layers and cold channel layers contains the same number ofhelical fluid channels. In the depicted example, each hot channel layer230 a-230 c contains twelve hot helical fluid channels 214, and eachcold channel layer 232 a-232 c contains twelve cold helical fluidchannels 220. Within examples, with any number of helical walls 240, thenumber of helical fluid channels 214 or 220 in each channel layer maymatch the number of helical walls 240. In the depicted example, centralsection 221 has a total of thirty-six hot helical fluid channels 214 andthirty-six cold helical fluid channels 220. Within examples, the heattransfer device may have a total of at least 4, 8, 12, 16, 20, 24, 28,32, 36, 40, or 50 helical fluid channels (each hot or cold), amongothers.

Each helical fluid channel 214, 220 is bounded by a pair of helicalwalls 240 and one or more of nested tubular walls 238 a-238 f (see FIGS.11 and 12 ). Each of hot helical fluid channels 214 of hot channellayers 230 a-230 c and cold helical fluid channels 220 of cold channellayers 232 a-232 c has a pair of rotationally-offset channel walls 248provided by an adjacent pair of helical walls 240. The same pair ofadjacent helical walls 240 forms the rotationally-offset channel walls248 of a helical column 253 of alternating hot and cold helical fluidchannels 214, 220. Each helical fluid channel 214 of hot channel layers230 a-230 c and each helical fluid channel 220 of cold channel layers232 b, 232 c has a pair of radially-spaced channel walls 250 provided byan adjacent pair of tubular walls of nested tubular walls 238 a-238 f.However, each helical fluid channel 220 of cold channel layer 232 a hasonly one wall that is formed by a tubular wall, namely, innermosttubular wall 238 a. More specifically, the helical fluid channels 220 ofcold channel layer 232 a are open helical passages 252 havingrotationally-offset channel walls 248 formed by protruding helical ribs244 at radially inner portions of helical walls 240. Each helicalpassage 252 is radially outward of and continuous with a linear corepassageway 262 that is coaxial with central axis 234 (also see FIGS. 4and 5 ). Within examples, helical walls 240 may not protrude into thelumen of the innermost nested tubular wall, and thus open helicalpassages 252 are not formed.

In the depicted example, the thickness of hot channel layers 230 a-230c, measured radially, is different from that of cold channel layers 232a-232 c (see FIGS. 9-12 ). The thickness of the hot channel layersrelative to the thickness of the cold channel layers can be selected tooptimize performance, such as to provide the desired ratio of hot andcold wetted surface areas, and/or to accommodate differences in theviscosity of the fluids, among others.

Each channel layer 230 a-230 c and 232 a-232 c has an inlet end 264opposite an outlet end 266 (see FIGS. 9, 10, 13, and 14 ). Inlet end 264of each hot channel layer 230 a-230 c is adjacent end section 222 b, andoutlet end 266 of each hot channel layer is adjacent end section 222 a(also see FIGS. 4 and 5 ). This arrangement is logical because endsection 222 b contains hot intake 210 and end section 222 a contains hotouttake 212. Accordingly, the positions of inlet end 264 and outlet end266 are switched for cold channel layers 232 a-232 c relative to hotchannel layers 230 a-230 c. More specifically, inlet end 264 of eachcold channel layer 232 a-232 c is adjacent end section 222 a, and outletend 266 of each cold channel layer 232 a-232 c is adjacent end section222 b. The inlet end 264 of each hot channel layer 230 a-230 c and coldchannel layer 232 a-232 c includes a channel inlet 268 of each helicalfluid channel 214 or 220 of the channel layer, and the outlet end 266 ofthe channel layer includes a channel outlet 270 of the helical fluidchannel.

Each manifold 223, 224, 226, 228 of heat transfer device 200 providesfluid communication between a port of the device (i.e., one of hotintake 210, hot outtake 212, cold intake 216, and cold outtake 218) andeach hot helical fluid channel 214 or each cold helical fluid channel220; see FIG. 9 . Manifolds 223, 224, 226, and 228 are similar instructure; corresponding features are identified with an appended letter“a” for parts of hot inflow manifold 223, “b” for parts of hot outflowmanifold 224, “c” for parts of cold inflow manifold 226, and “d” forparts of cold outflow manifold 228.

Each manifold includes a plenum, namely, a hot inflow plenum 272 a, ahot outflow plenum 272 b, a cold inflow plenum 272 c, or a cold outflowplenum 272 d. Each plenum 272 a-272 d directly communicates with thecorresponding port, but directly communicates with only a subset of thechannel inlets 268 or channel outlets 270 of helical fluid channels 214or helical fluid channels 220 of each channel layer. In the depictedexample, each plenum directly communicates with only one-half (six) ofthe channel inlets or channel outlets of the helical fluid channels ofeach corresponding hot or cold channel layer.

Inflow manifolds 223, 226 also include distribution channels 274 a ordistribution channels 274 c, respectively (see FIGS. 9, 10, 13, and 14). Each distribution channel 274 a of inflow manifold 223 provides fluidcommunication between inflow plenum 272 a and channel inlets 268 of oneof the remaining subsets of hot helical fluid channels 214 of one of hotchannel layers 230 a-230 c, where the remaining subset is laterallyoffset from, and not in direct fluid communication with, the inflowplenum. Similarly, each distribution channel 274 c of inflow manifold226 provides fluid communication between inflow plenum 272 c and channelinlets 268 of one of the remaining subsets of cold helical fluidchannels 220 of one of cold channel layers 232 a-232 c, where theremaining subset is laterally offset from, and not in direct fluidcommunication with, the inflow plenum.

Outflow manifolds 224, 228 also include collection channels 274 b orcollection channels 274 d, respectively (see FIGS. 9, 10, 13, and 14 ).Each collection channel 274 b of outflow manifold 224 provides fluidcommunication between outflow plenum 272 b and channel outlets 270 ofone of the remaining subsets of hot helical fluid channels 214 of one ofhot channel layers 230 a-230 c, where the remaining subset is laterallyoffset from, and not in direct fluid communication with, the outflowplenum. Similarly, each distribution channel 274 d of outflow manifold228 provides fluid communication between plenum 272 d and channeloutlets 270 of one of the remaining subsets of cold helical fluidchannels 220 of one of cold channel layers 232 a-232 c, where theremaining subset is laterally offset from, and not in direct fluidcommunication with, the outflow plenum.

Each distribution channel 274 a, 274 c and each collection channel 274b, 274 d is at least partially bounded by a corresponding end cap (seeFIGS. 9, 13, and 14 ). Distribution channels 274 a are at leastpartially bounded by end caps 276 a. Distribution channels 274 c are atleast partially bounded by end caps 276 c. Collection channels 274 b areat least partially bounded by end caps 276 b. Collection channels 274 dare at least partially bounded by end caps 276 d. Each distributionchannel 274 a, each collection channel 274 b, each of two of threedistribution channels 274 c, and each of two of three collectionchannels 274 d defines an arcuate longitudinal axis that extends along asemicircular portion of the inlet end or the outlet end of a hot or coldchannel layer, and along a plane that is orthogonal to the longitudinalaxis of the heat transfer device.

Each inlet end 264 and each outlet end 266 of each channel layer 230a-230 c and 232 a-232 c has an aligned portion 278 and an offset portion280. Channel inlets 268 or channels outlets 270 of aligned portion 278are axially aligned with, and directly communicate with, thecorresponding plenum 272 a, 272 b, 272 c, or 272 d. Channel inlets 268or channels outlets 270 of offset portion 280 are laterally offset fromthe corresponding plenum, and are axially aligned instead with anadjacent plenum. Each end cap 276 a-276 d forms a wall of acorresponding distribution channel 274 a or 274 c, or correspondingcollection channel 274 b or 274 d, and separates the adjacent plenumfrom the corresponding distribution or collection channel.

FIGS. 13 and 14 show flow paths 202, 204 of the first and second fluidswith respect to manifolds 223, 224, 226, and 228. The line weights ofarrows representing each flow path decrease as the flow path entersdistribution channels 274 a or 274 c from the corresponding inflowplenum 272 a or 272 c, or increases as the flow path enters an outflowplenum 272 b or 272 d from corresponding collection channels 274 b or274 d.

Outermost tubular wall 238 f also forms a cylindrical portion of ahousing 282 (interchangeably called a shell) of heat transfer device 200(see FIGS. 9 and 10 ). Accordingly, the outermost tubular wall 238 f hasa thicker wall than the other tubular walls 238 a-238 e of the set ofnested tubular walls, to make heat transfer device 200 more capable ofwithstanding large pressure differences between the inside and theoutside of the device. The wall of outermost tubular wall 238 f smoothlytransitions to a peripheral wall of each end section 222 a, 222 b (seeFIG. 9 ).

In the present example, all components of heat transfer device 200 areadditively manufactured as a single monolithic unit. Such unitarityreduces part count and production time over conventionally manufacturedheat exchangers. Such unitarity also reduces overall weight and volumeof the heat transfer device by eliminating constraints of traditionalmanufacturing. Unitarity and use of a single material in printing alsoimproves heat transfer performance by eliminating joints and interfacesand maximizing wetted surface area. Additive manufacturing also allowsshapes and structures optimal for heat transfer that are not achievablein traditional manufacturing.

An example of heat transfer device 200, intended for illustration only,has a 100 kW heat transfer capacity. The exemplary device has a mass ofabout 45 pounds (20.4 kilograms) and is formed of a nickel-based alloy.The cold wetted surface area is about 1350 square inches (0.87 squaremeter), and the hot wetted surface area is about 1690 square inches(1.10 square meter). The outer diameter is 7.45 inches (0.19 meter), theoverall length is 17 inches (0.43 meter), and the working length is 9.2inches (0.23 meter).

C. Heat Transfer Devices with Protrusions in Helical Fluid Channels

This subsection describes illustrative heat transfer devices 300, 400,and 500 having protrusions each projecting into the lumen of a helicalfluid channel; see FIGS. 15-17 . The protrusions are enhancements to theheat transfer surfaces of the helical fluid channels and may improve theefficiency of heat transfer between the fluid channels, potentiallyallowing the heat transfer device to be more compact.

FIG. 15 shows a fragmentary, sectional portion of heat transfer device300, which is identical to heat transfer device 200 of subsection B,except for the addition of protrusions 386 (compare with FIG. 11 ). Heattransfer device 300 has hot helical fluid channels 314 and cold helicalfluid channels 320, which correspond in number and position to hothelical fluid channels 214 and cold helical fluid channels 220 of heattransfer device 200. Each helical fluid channel 314 or helical fluidchannel 320 has a lumen 388 and contains a pair of protrusions 386. Eachprotrusion 386 of the pair projects into the lumen from a helical wall340, to a free edge of the protrusion that is spaced from the walls ofthe helical fluid channel. The pair of protrusions 386 project into thelumen from a pair of helical walls 340 that are rotationally adjacentone another.

FIG. 16 shows a fragmentary, sectional portion of heat transfer device400, which is identical to heat transfer device 200 of subsection B,except for the addition of protrusions 486 (compare with FIG. 11 ). Heattransfer device 400 has hot helical fluid channels 414 and cold helicalfluid channels 420, which correspond in number and position to hothelical fluid channels 214 and cold helical fluid channels 220 of heattransfer device 200. Each hot helical fluid channel 414 and each coldhelical fluid channel 420 has a lumen 488 and contains a pair ofprotrusions 486. Each protrusion 486 of the pair projects into the lumenfrom a helical wall 440, to a free edge of the protrusion that is spacedfrom the walls of the helical fluid channel. The pair of protrusions 486project into the lumen from a pair of helical walls 440 that arerotationally adjacent one another. Protrusions 486 are similar toprotrusions 386 of heat transfer device 300, except that they areradially offset from one another within a given helical fluid channel,which can improve mixing of fluid in the helical fluid channel.

FIG. 17 shows a fragmentary, sectional portion of heat transfer device500, which is identical to heat transfer device 200 of subsection B,except for the addition of protrusions 586 (compare with FIG. 11 ). Heattransfer device 500 has hot helical fluid channels 514 and cold helicalfluid channels 520, which correspond in number and position to hothelical fluid channels 214 and cold helical fluid channels 220 of heattransfer device 200. Heat transfer device 500 also has nested tubularwalls 538 a-538 f and helical walls 540, which intersect to bound thehot helical fluid channels and the cold helical fluid channels, asdescribed above for heat transfer device 200. Each hot helical fluidchannel 514 and each cold helical fluid channel 520 has a lumen 588 anda pair of protrusions 586. Each protrusion 586 of the pair projectsradially into the lumen of a given helical fluid channel from a tubularwall of nested tubular walls 538 a-538 f, to a free edge of theprotrusion that is spaced from the walls of the helical fluid channel.The pair of protrusions 586 project into the lumen from a pair ofadjacent tubular walls of the nested tubular walls 538 a-538 f.

The protrusions of this example may be elongated along the helical fluidchannels to form flanges (interchangeably called ribs), which may behelical flanges. Each helical flange may extend along at least a portionof a helical path followed by a corresponding helical fluid channel(s).However, in the other examples, the flanges may be non-helical. Theprotrusions in each of the heat transfer devices of this subsectionimprove the efficiency of heat transfer by increasing the wetted surfacearea of conductive material of the heat transfer device that is incontact with each of the fluids. In other examples, only one or morethan two protrusions project into the lumen of a given helical fluidchannel. In other examples, two protrusions project into the lumen fromthe same helical wall or the same tubular wall, or from a helical walland a tubular wall. In other examples, the protrusions are present inonly a subset of the channel layers, such as only the hot channel layersor only the cold channel layers.

D. Heat Transfer Device with Openings in a Helical Wall

This subsection describes an illustrative heat transfer device 600having a helical wall defining at least one opening that provides fluidcommunication, mixing, and heat transfer between a pair of adjacenthelical fluid channels within a channel layer; see FIG. 18 .

FIG. 18 shows a fragmentary, sectional portion of heat transfer device600, which is identical to heat transfer device 200 of subsection B,except for the addition of openings 690 in a helical wall 640 (comparewith FIG. 11 ). Heat transfer device 600 has hot helical fluid channels614 and cold helical fluid channels 620, which correspond in number andposition to hot helical fluid channels 214 and cold helical fluidchannels 220 of heat transfer device 200.

Each opening 690 extends through helical wall 640 to each of a pair ofadjacent hot helical fluid channels 614 or cold helical fluid channels620 in the same channel layer, and thus interchangeably is described asa through-opening or through-hole. Each opening is circular. However, inother examples, the opening can be non-circular, such as a helicalopening elongated along a helical path followed by the helical wall, orelongated transverse to the helical path, among others. With anysuitable geometry, the opening provides fluid communication between thepair of adjacent channels at a position intermediate the inlets andoutlets of the pair of channels. Openings 690 can improve the efficiencyof the heat transfer device by encouraging mixing between adjacentchannels. In other examples, openings 690 are formed in two or morehelical walls, such as each helical wall 640. The openings can decreasethe weight of the device because the openings in a helical wall make thewall lighter. In some examples, two or more openings 690 provide fluidcommunication between a given helical fluid channel and an adjacenthelical fluid channel, at two or more positions along the given helicalfluid channel.

E. Aerospace Vehicle Including a Heat Transfer Device

This subsection describes an illustrative aerospace vehicle 700including heat transfer device 100, which is incorporated in a powercycle; see FIG. 19 (also see FIGS. 1 and 2 and the Overview sectionabove).

Aerospace vehicle 700 has a vehicle body 701 and an engine 703 connectedto the vehicle body and configured to power the vehicle body in a flightmode. The vehicle body can include a fuselage and one or more airfoils,such as wings. The aerospace vehicle can be an aircraft, a spacecraft, arotorcraft, a missile, or a combination thereof, among others. Engine703 provides propulsion for the vehicle and can, for example, be anairbreathing jet engine (such as a turbojet, turbofan, ramjet, or pulsejet engine), a rocket engine, a propeller/rotor engine, or the like.

Heat transfer device 100 is connected to vehicle body 701 and/or engine703. The heat transfer device can be utilized to transfer heat betweenany suitable first fluid 106 and second fluid 108. In the exampledepicted, heat transfer device 100 transfers heat from air 705, as firstfluid 106, to supercritical carbon dioxide (SCCD) 707, as second fluid108. In other examples, heat transfer device 100 onboard aerospacevehicle 700 transfers heat from oil to air, air to air, water/steam toair, oil to water/steam, air to fuel, water/steam to fuel, or viceversa, among others.

The first flow path 102 of heat transfer device 100 is in fluidcommunication with an engine intake 709 of engine 703. Air 705 entersengine intake 709 from outside aerospace vehicle 700 and has a hightemperature due to the speed of the vehicle, which may be a hypersonicairplane. The air is cooled by passing it through heat transfer device100 on first flow path 102, before entering a combustion chamber(s) ofengine 703. The air may be cooled upstream of a fan or compressor stageof the engine, to mitigate the risk of heat damage. Cooling air upstreamof the engine's combustion chamber could have two effects: limitingengine performance, and preventing damage to downstream enginecomponents such as turbines or exhaust nozzles. In other examples,instead of entering an engine intake, the air enters an intake of anenvironmental control system of the aerospace vehicle.

SCCD 707 can be used as the working fluid in a thermodynamic cycle toconvert heat to another form of energy, such as electrical, mechanical,and/or chemical energy. The second flow path 104 of heat transfer device100 is in fluid communication with a turbine 711, a heat exchanger 713,and a compressor 715 of a heat-to-power thermodynamic cycle. Rotation ofturbine 711 is driven by SCCD 707 received from heat transfer device 100after the SCCD 707 has been heated with thermal energy received from air705. The rotation of turbine 711 drives a generator 717, which convertsmechanical energy to electrical energy. The electrical energy can bestored or used directly. Rotation of the turbine also powers compressor715, which compresses SCCD 707 after additional thermal energy has beenremoved by heat exchanger 713. The compressed SCCD 707 then flows backto heat transfer device 100 and the cycle is repeated.

F. Power Plant Including a Heat Transfer Device

This subsection describes an illustrative power plant 800 including heattransfer device 100, which is incorporated in a heat-to-powerthermodynamic cycle; see FIG. 20 (also see FIGS. 1 and 2 and theOverview section above).

The power cycle transfers heat from a first fluid 106, such as steam,flowing through heat transfer device 100 on first flow path 102, to asecond fluid 108, such as supercritical carbon dioxide (SCCD) 807, onsecond flow path 104. The first fluid is heated by a heat source 819upstream of heat transfer device 100. The heated second fluid flows in aclosed loop from second flow path 104 of heat transfer device 100through a turbine 811, a heat exchanger 813, and a compressor 815, andback to heat transfer device 100, as described above in subsection E.Rotation of turbine 811 drives a generator 817 as explained above insubsection E.

G. Method of Transferring Heat

This subsection describes steps of an illustrative method 900 oftransferring heat between fluids using a heat transfer device havinghelical fluid channels; see FIG. 21 . Aspects of heat transfer devicesdescribed above may be utilized in the method steps described below.Where appropriate, reference may be made to components and systems thatmay be used in carrying out each step. These references are forillustration, and are not intended to limit the possible ways ofcarrying out any particular step of the method. Although various stepsof method 900 are described below and depicted in FIG. 21 , the stepsneed not necessarily all be performed, and in some cases may beperformed simultaneously or in a different order than the order shown,and the method may not recite the complete process or all steps of themethod.

At step 902, a first fluid is passed through a heat transfer device. Theheat transfer device has any suitable combination of elements andfeatures described elsewhere herein.

At step 904, a second fluid is passed through the heat transfer device.The first and second fluids pass through the heat transfer device at thesame time, but without contacting one another. The first and secondfluids pass through the heat transfer device in opposite directions fromone another, on respective helical paths that may be concentric with,and parallel to, one another.

At step 906, heat is transferred between the first and second fluids,such that the second fluid is heated and the first fluid is cooled.

At step 908, the heated second fluid is used to operate a turbine. Theheated second fluid passes through the turbine to produce rotationthereof.

At step 910, electrical energy is generated using mechanical energy fromthe turbine.

H. Illustrative Aerospace Vehicles and Associated Method

Examples disclosed herein may be described in the context of anillustrative aircraft or aerospace vehicle 1000 (see FIG. 22 ) and anillustrative aerospace vehicle manufacturing and service method 1100(see FIG. 23 ). Method 1100 includes a plurality of processes, stages,or phases. During pre-production, method 1100 may include aspecification and design phase 1104 of aerospace vehicle 1000 and amaterial procurement phase 1106. During production, a component andsubassembly manufacturing phase 1108 and a system integration phase 1110of aerospace vehicle 1000 may take place. Thereafter, aerospace vehicle1000 may go through a certification and delivery phase 1112 to be placedinto in-service phase 1114. While in service (e.g., by an operator),aerospace vehicle 1000 may be scheduled for routine maintenance andservice phase 1116 (which may also include modification,reconfiguration, refurbishment, and so on of one or more systems ofaerospace vehicle 1000). While the examples described herein relategenerally to the production and operational use of aerospace vehicle1000, they may be practiced at other stages of method 1100.

Each of the processes of method 1100 may be performed or carried out bya system integrator, a third party, and/or an operator (e.g., acustomer). For the purposes of this description, a system integrator mayinclude, without limitation, any number of aerospace vehiclemanufacturers and major-system subcontractors; a third party mayinclude, without limitation, any number of vendors, subcontractors, andsuppliers; and an operator may be an airline, leasing company, militaryentity, service organization, and so on.

As shown in FIG. 22 , aerospace vehicle 1000 produced by illustrativemethod 1100 may include a frame 1002 with a plurality of systems 1004and an interior 1006. Examples of plurality of systems 1004 include oneor more of an engine system 1008, an electrical system 1010, a hydraulicsystem 1012, an environmental control system 1014, and a flight controlsystem 1016. Each system may comprise various subsystems, such ascontrollers, processors, actuators, effectors, motors, generators, etc.,depending on the functionality involved. Any number of other systems maybe included. The engine system 1008 includes an engine connected to theaerospace vehicle body and configured to power the aerospace vehiclebody in a flight mode. Electrical system 1010 and/or environmentalcontrol system 1014 of aerospace vehicle 1000 includes a heat transferdevice. For instance, in an example, aerospace vehicle 1000 includesheat transfer device 100, 200, 300, 400, 500, or 600.

Although an aerospace example is shown, the principles disclosed hereinmay be applied to other industries, such as the power industry,automotive industry, rail transport industry, and nautical engineeringindustry. Accordingly, in addition to aerospace vehicle 1000, theprinciples disclosed herein may apply to other vehicles, e.g., landvehicles, marine vehicles, etc.

Apparatuses and methods shown or described herein may be employed duringany one or more of the stages of the aerospace vehicle manufacturing andservice method 1100. For example, components or subassembliescorresponding to component and subassembly manufacturing phase 1108 maybe fabricated or manufactured in a manner similar to components orsubassemblies produced while aerospace vehicle 1000 is operating duringin-service phase 1114. Also, one or more examples of the apparatuses,methods, or combinations thereof may be utilized during manufacturingphase 1108 and system integration phase 1110, for example, bysubstantially expediting assembly of or reducing the cost of aerospacevehicle 1000. Similarly, one or more examples of the apparatus or methodrealizations, or a combination thereof, may be utilized, for example andwithout limitation, while aerospace vehicle 1000 is in in-service phase1114 and/or during maintenance and service phase 1116.

Illustrative Combinations and Additional Examples

This section describes additional aspects and features of heat transferdevices with helical fluid channels, presented without limitation as aseries of paragraphs, some or all of which may be alphanumericallydesignated for clarity and efficiency. Each of these paragraphs can becombined with one or more other paragraphs, and/or with disclosure fromelsewhere in this application, in any suitable manner. Some of theparagraphs below expressly refer to and further limit other paragraphs,providing without limitation examples of some of the suitablecombinations.

A1. A device for transferring heat between a first fluid and a secondfluid, the device comprising: (i) a set of nested tubular walls; (ii) aplurality of helical walls intersecting each of the nested tubular wallsto form one or more first channel layers nested with one or more secondchannel layers, each first channel layer and each second channel layerincluding a plurality of helical fluid channels; (iii) a first intakeand a first outtake in fluid communication with one another via theplurality of helical fluid channels of each first channel layer, forflow of the first fluid through the device from the first intake to thefirst outtake; and (iv) a second intake and a second outtake in fluidcommunication with one another via the plurality of helical fluidchannels of each second channel layer, for flow of the second fluidthrough the device from the second intake to the second outtake.

A2. The device of paragraph A1, wherein each helical fluid channel ofthe plurality of helical fluid channels of each first channel layer andeach second channel layer has a pair of channel walls formed by a pairof helical walls of the plurality of helical walls, and wherein,optionally, the pair of channel walls are rotationally offset from oneanother about a central axis defined by the set of nested tubular walls.

A3. The device of paragraph A1 or A2, wherein each helical fluid channelof the plurality of helical fluid channels of at least one first channellayer and at least one second channel layer has a pair of channel wallsspaced radially from one another and formed by a pair of nested tubularwalls of the set of nested tubular walls.

A3.1. The device of any of paragraphs A1 to A3, wherein each helicalfluid channel of the plurality of helical fluid channels of each firstchannel layer and each second channel layer is bounded by a pair of thenested tubular walls and a pair of the helical walls.

A4. The device of any of paragraphs A1 to A3.1, wherein the one or morefirst channel layers and the one or more second channel layers arearranged in a radial series of at least two first channel layersalternating with at least two second channel layers.

A4.1. The device of any of paragraphs A1 to A4, wherein a radialthickness of each first channel layer is different from a radialthickness of each second channel layer.

A5. The device of any of paragraphs A1 to A4.1, wherein the helicalwalls of the plurality of helical walls have the same helical leadand/or the same radius as one another.

A6. The device of any of paragraphs A1 to A5, wherein the set of nestedtubular walls includes an outermost tubular wall forming at least partof a periphery of the device and at least three, four, or five nestedtubular walls of successively smaller diameter inside the outermosttubular wall.

A6.1. The device of paragraph A6, wherein the outermost tubular wall hasa greater thickness, measured radially than each other nested tubularwall of the set of nested tubular walls.

A7. The device of any of paragraphs A1 to A6.1, wherein the set ofnested tubular walls, the plurality of helical walls, the first andsecond intakes, and the first and second outtakes are formedcollectively as a single monolithic unit.

A8. The device of any of paragraphs A1 to A7, wherein at least one ofthe first intake and the second intake includes one or moreflow-steering vanes configured to encourage swirling flow of fluidpassing through the at least one of the first intake and the secondintake.

A9. The device of any of paragraphs A1 to A8, further comprising a firstinflow manifold providing fluid communication between the first intakeand each helical fluid channel of the plurality of helical fluidchannels of each first channel layer, the first inflow manifoldincluding a plenum and a distribution channel extending from the plenum,the plenum being in direct fluid communication with only a subset of theplurality of helical fluid channels of a first channel layer of the oneor more first channel layers, the distribution channel providing fluidcommunication between the plenum and another subset of the plurality ofhelical fluid channels of the first channel layer of the one or morefirst channel layers.

A9.1. The device of paragraph A9, wherein the first inflow manifoldincludes a respective distribution channel for each first channel layer.

A9.2. The device of paragraph A9 or A9.1, the plenum being a firstinflow plenum, further comprising a second inflow manifold providingfluid communication between the second intake and each helical fluidchannel of the plurality of helical fluid channels of each secondchannel layer, the second inflow manifold including a second inflowplenum and a second distribution channel extending from the secondinflow plenum, the second inflow plenum being in direct fluidcommunication with only a subset of the plurality of helical fluidchannels of a second channel layer of the one or more second channellayers, the second distribution channel providing fluid communicationbetween the second inflow plenum and another subset of the plurality ofhelical fluid channels of the second channel layer of the one or moresecond channel layers

A10. The device of any of paragraphs A9 to A9.2, further comprising: asecond outflow manifold located adjacent the first inflow manifold andincluding an outflow plenum, the second outflow manifold providing fluidcommunication between each helical fluid channel of the plurality ofhelical fluid channels of each second channel layer and the secondouttake; and an end cap located at an inlet end of the first channellayer of the one or more first channel layers, the end cap forming awall of the distribution channel and separating the outflow plenum ofthe second outflow manifold from the distribution channel of the firstinflow manifold.

A11. The device of any of paragraphs A1 to A10, wherein the set ofnested tubular walls defines a central axis, and wherein the firstintake, the first outtake, the second intake, and the second outtakedefine respective axes that are parallel to the central axis.

A12. The device of paragraph A11, wherein the respective axes arecoplanar with one another.

A13. The device of any of paragraphs A1 to A12, wherein each helicalwall of the plurality of helical walls provides a load path extendingradially and continuously from an outermost tubular wall to an innermosttubular wall of the set of nested tubular walls.

A14. The device of any of paragraphs A1 to A13, further comprising aflange projecting from a helical wall of the plurality of helical walls,or from a nested tubular wall of the set of nested tubular walls, andinto a lumen of a helical fluid channel of the plurality of helicalfluid channels of a first channel layer or a second channel layer.

A14.1 The device of paragraph A14, wherein the flange is a helicalflange.

A14.2. The device of paragraph A14 or A14.1, further comprising aplurality of flanges each projecting from the same helical wall of theplurality of helical walls, or from the same tubular wall of the set ofnested tubular walls, into a lumen of a helical fluid channel of theplurality of helical fluid channels of a first channel layer or a secondchannel layer.

A15. The device of any of paragraphs A1 to A14.2, wherein each helicalwall of at least a subset of the plurality of helical walls projectsinto a lumen of an innermost nested tubular wall of the set of nestedtubular walls such that the at least a subset of the plurality ofhelical walls forms a plurality of open helical passages that are influid communication with one another within the innermost tubular walland in fluid communication with one of the first and second intakes anda corresponding one of the first and second outtakes.

A16. The device of any of paragraphs A1 to A15, further comprising afirst inflow manifold providing fluid communication between the firstintake and the plurality of helical fluid channels of each first channellayer, the first inflow manifold including an inflow plenum and adistribution channel, the distribution channel being located at an inletend of a first channel layer and directing fluid from the plenum tochannel inlets of only a subset of the plurality of helical fluidchannels of the first channel layer.

A16.1. The device of paragraph A16, wherein the distribution channeldefines a longitudinal axis lying in a plane that is orthogonal to acentral axis of the set of nested tubular walls.

A16.2. The device of paragraph A16 or A16.1, wherein the one or morefirst channel layers include two or more first channel layers, andwherein the first inflow manifold includes a respective distributionchannel for each first channel layer of the two or more first channellayers.

A16.3. The device of any of paragraphs A16 to A16.2, wherein anothersubset of the plurality of helical fluid channels of the first channellayer has channel inlets that communicate directly with the inflowplenum of the first inflow manifold.

A16.4. The device of any of paragraphs A16 to A16.3, wherein an offsetportion of an inlet end of each first channel layer is covered by an endcap, and wherein an aligned portion of the inlet end of each firstchannel layer communicates directly with the inflow plenum.

A16.5. The device of paragraph A16.4, wherein the offset portion of theinlet end of each first channel layer is offset from the plenum in adirection transverse to a central axis of the set of nested tubularwalls, and wherein the aligned portion of the inlet end of each firstchannel layer is aligned with the inflow plenum along a line parallel tothe central axis.

A17. The device of any of paragraphs A1 to A16.5, wherein the device hasa central section located between a pair of end sections, wherein thecentral section includes each of the first and second channel layers,wherein the first intake and the second outtake are provided by one ofthe end sections, and wherein the second intake and the first outtakeare provided by the other of the end sections.

A18. The device of any of paragraphs A1 to A17, wherein the device isconfigured to provide counterflow of the first and second fluids throughthe device on respective first and second flow paths that are not influid communication with one another.

A19. The device of any of paragraphs A1 to A18, further comprising aprotrusion projecting from a helical wall of the plurality of helicalwalls or from a nested tubular wall of the set and nested tubular walls,into a lumen of a helical fluid channel of the plurality of helicalfluid channels of a first channel layer or a second channel layer.

A20. The device of paragraph A19, wherein two or more protrusionscollectively project into a lumen of each of two or more helical fluidchannels of the plurality of helical fluid channels of one or morechannel layers of the first and second channel layers from one of thehelical walls, optionally from the same helical wall, optionally intothe same first or second channel layer, optionally into at least twochannel layers of the first and second channel layers.

A21. The device of paragraph A20, wherein the two or more protrusionsare two or more helical flanges that collectively project into the lumenof each of the two or more of the helical fluid channels from one of thehelical walls.

A22. The device of any of paragraphs A1 to A21, wherein the plurality ofhelical fluid channels of a first channel layer of the one or more firstchannel layers includes a pair of adjacent helical fluid channels havinga pair of channel inlets and a pair of channel outlets, and wherein oneof the helical walls defines an opening that provides fluidcommunication between the pair of adjacent helical fluid channels at aposition intermediate the pair of channel inlets and the pair of channeloutlets.

A23. The device of any of paragraphs A1 to A22, wherein each firstchannel layer is located between an adjacent pair of the tubular walls,and wherein each second channel layer is located between an adjacentpair of the tubular walls.

A24. The device of any of paragraphs A1 to A23, wherein each firstchannel layer is radially adjacent a second channel layer, and whereineach second channel layer is radially adjacent a first channel layer.

A25. The device of any of paragraphs A1 to A24, wherein the helicalwalls of the plurality of helical walls are rotationally offset from oneanother about a central axis defined by the set of nested tubular walls.

A26. The device of paragraphs A25, wherein the helical walls of theplurality of helical walls have a uniform rotational offset from oneanother about the central axis.

A27. The device of any of paragraphs A1 to A26, wherein the plurality ofhelical walls includes at least three, four, five, six, eight, or tenhelical walls.

A28. An aerospace vehicle comprising the device of any of paragraphs A1to A27.

A29. A power plant comprising the device of any of paragraphs A1 to A27.

A30. The aerospace vehicle or power plant of paragraph A28 or A29,wherein the device is in fluid communication with a turbine.

A31. The device of any of paragraphs A1 to A27, wherein the device isconfigured to receive and heat supercritical carbon dioxide as a workingfluid in a thermodynamic cycle.

B1. An aerospace vehicle comprising: (i) a vehicle body; (ii) an engineconnected to the vehicle body and configured to power the vehicle bodyin a flight mode; and (iii) a heat transfer device connected to thevehicle body and/or the engine and including a set of nested tubularwalls, a plurality of helical walls intersecting each of the nestedtubular walls to form one or more first channel layers nested with oneor more second channel layers, each first channel layer and each secondchannel layer including a plurality of helical fluid channels, a firstintake and a first outtake in fluid communication with one another viathe helical fluid channels of each first channel layer, for flow of afirst fluid through the heat transfer device from the first intake tothe first outtake, and a second intake and a second outtake in fluidcommunication with one another via the plurality of helical fluidchannels of each second channel layer, for flow of a second fluidthrough the heat transfer device from the second intake to the secondouttake.

B2. The aerospace vehicle of paragraph B1, wherein the heat transferdevice is configured to cool intake air for the engine.

B3. The aerospace vehicle of paragraph B1 or B2, wherein one of thefirst and second fluids is supercritical carbon dioxide.

B4. The aerospace vehicle of paragraph B3, wherein the heat transferdevice is configured to heat the supercritical carbon dioxide for use asa working fluid in a thermodynamic cycle that converts heat to anotherform of energy.

B5. The aerospace vehicle of any of paragraphs B1 to B4, wherein theheat transfer device is in fluid communication with a turbine.

B6. The aerospace vehicle of any of paragraphs B1 to B5, wherein theaerospace vehicle is a hypersonic airplane.

B7. The aerospace vehicle of any of paragraphs B1 to B6, wherein theheat transfer device includes any limitation or combination oflimitations of paragraphs A1 to A27 and A31.

C1. A method of transferring heat between fluids using a heat transferdevice including a set of nested tubular walls intersected by aplurality of helical walls to form one or more first channel layersnested with one or more second channel layers, the method comprising:(i) passing a first fluid through the heat transfer device between afirst intake and a first outtake via a plurality of helical fluidchannels of each of one or more first channel layers of the heattransfer device; and (ii) passing a second fluid through the heattransfer device between a second intake and a second outtake via aplurality of helical fluid channels of each of one or more secondchannel layers of the heat transfer device.

C2. The method of paragraph C1, wherein passing a first fluid includespassing a first fluid through a plurality of helical fluid channelsdefined by each of at least two first channel layers of the device, andwherein passing a second fluid includes passing a second fluid through aplurality of helical fluid channels defined by each of at least twosecond channel layers of the device.

C3. The method of paragraph C1 or C2, wherein the heat transfer deviceincludes any limitation or combination of limitations of paragraphs A1to A27 and A31.

D1. A device for transferring heat between a first fluid and a secondfluid, the device comprising: (i) a central section forming a radialseries of first channel layers alternating with second channel layers,each of the first and second channel layers defining a plurality ofhelical fluid channels, wherein the central section includes a pluralityof concentric helical walls, and wherein each helical fluid channel ofthe plurality of helical fluid channels of each first and second channellayer has a pair of walls formed by a pair of the helical walls; (ii) afirst intake and a first outtake in fluid communication with one anothervia the plurality of helical fluid channels of each first channel layer,for flow of the first fluid through the device; and (iii) a secondintake and a second outtake in fluid communication with one another viathe plurality of helical fluid channels of each second channel layer,for flow of the second fluid through the device.

D2. The device of paragraph D1, wherein the device includes anylimitation or combination of limitations of paragraphs A1 to A27 andA31.

Advantages, Features, and Benefits

The different examples of the heat transfer device described hereinprovide various advantages over traditional counterflow heat exchangers.The examples disclosed herein may be more compact and/or lighter inweight, may have more wetted surface area per unit volume for heattransfer and thus a greater efficiency of heat transfer, may handle anddistribute stress more efficiently, may provide more uniform fluid flow,may offer better mixing within a fluid, and/or may have fewer sharpturns, if any, along each fluid flow path.

Additionally, and among other benefits, illustrative examples describedherein provide more efficient pressure containment. The outermosttubular wall may be cylindrical, which takes advantage of inherent hoopstrength to handle a large pressure differential between the outermostlayer of helical fluid channels and the ambient environment outside theheat transfer device. The tubular walls nested in the outermost tubularwall also may be cylindrical, which also takes advantage of inherenthoop strength to provide the capability to handle a large pressuredifferential between adjacent hot and cold layers of helical fluidchannels. End caps may be located at the inlet and outlet ends of eachchannel layer, and may be rounded/domed to avoid points of concentratedstress (stress risers) in response to pressure differentials. Helicalwalls may provide radial load paths each extending from the exteriorsurface of the heat transfer device to the innermost tubular wall, suchthat each helical wall efficiently reacts to pressure differentials intension and the helical walls can collectively react to high pressuredifferentials.

Additionally, and among other benefits, the helical walls ofillustrative examples described herein offer unique characteristics andadvantages. The helical walls function not only as efficient structuralmembers but also transfer heat between hot and cold helical fluidchannels, thereby increasing the wetted surface area for heat transferand thus the efficiency of heat transfer. Moreover, the number, helicalpitch, and helical lead of the helical walls can be selected tocustomize the performance of the heat transfer device. Increasing thenumber of helical walls, decreasing the helical pitch of the helicalwalls, and decreasing the helical lead of each helical wall, increasesthe wetted surface area within the device and the pressure-handlingcapacity of the device, without changing the length of the heat transferdevice. Alternatively, decreasing the number of helical walls,increasing the helical pitch of the helical walls, and/or increasing thehelical lead of each helical fin reduces the pressure drop through thedevice, without changing the length of the heat transfer device.

Additionally, and among other benefits, illustrative examples describedherein are strengthened substantially with only minimal increases in thethickness of the nested tubular walls and/or the helical walls.

Additionally, and among other benefits, illustrative examples describedherein have helical walls and/or tubular walls from which added features(protrusions) project, to increase the wetted surface area for heattransfer.

Additionally, and among other benefits, the fluid flow paths ofillustrative examples described herein have no sharp bends, therebyprovide a low pressure-drop design.

Additionally, and among other benefits, the intakes, outtakes, andmanifolds of illustrative examples described herein have a simplifiedconfiguration. The intakes and outtakes may be located at opposite endsof the heat transfer device, and may be parallel and coplanar with oneanother, and parallel to the longitudinal/central axis of the heattransfer device. This straight-in/straight-out configuration reduces thepressure drop relative to traditional counterflow heat exchangers havingelbow interfaces. Each manifold may be configured to communicate withmultiple channel layers each containing multiple helical fluid channels,and the same manifold configuration can communicate with any number ofchannels in a channel layer.

Additionally, and among other benefits, illustrative examples describedherein have intakes including swirl initiators that promote smootherintroduction of fluids into the channel inlets of helical fluidchannels, by creating rotational flow that matches the rotationaldirection of the helical fluid channels and directs fluid flow intobetter alignment with the channel inlets, while encouraging mixingwithin each fluid.

Additionally, and among other benefits, illustrative examples describedherein optimize fluid flow for enhanced heat transfer and reduced fluidpressure drop.

No known system or device can perform these functions, particularly withreduced weight and a smaller footprint than traditional heat transferdevices. Thus, the illustrative examples described herein areparticularly useful for aerospace vehicles. However, not all examplesdescribed herein provide the same advantages or the same degree ofadvantage.

CONCLUSION

The disclosure set forth above may encompass multiple distinct exampleswith independent utility. Although each of these has been disclosed inits preferred form(s), the specific examples thereof as disclosed andillustrated herein are not to be considered in a limiting sense, becausenumerous variations are possible. To the extent that section headingsare used within this disclosure, such headings are for organizationalpurposes only. The subject matter of the disclosure includes all noveland nonobvious combinations and subcombinations of the various elements,features, functions, and/or properties disclosed herein. The followingclaims particularly point out certain combinations and subcombinationsregarded as novel and nonobvious. Other combinations and subcombinationsof features, functions, elements, and/or properties may be claimed inapplications claiming priority from this or a related application. Suchclaims, whether broader, narrower, equal, or different in scope to theoriginal claims, also are regarded as included within the subject matterof the present disclosure.

What is claimed is:
 1. A device for transferring heat between a firstfluid and a second fluid, the device comprising: a set of nested tubularwalls; a plurality of helical walls intersecting each of the nestedtubular walls to form one or more first channel layers nested with oneor more second channel layers, each first channel layer and each secondchannel layer including a plurality of helical fluid channels; a firstintake and a first outtake in fluid communication with one another viathe plurality of helical fluid channels of each first channel layer, forflow of the first fluid through the device from the first intake to thefirst outtake; and a second intake and a second outtake in fluidcommunication with one another via the plurality of helical fluidchannels of each second channel layer, for flow of the second fluidthrough the device from the second intake to the second outtake.
 2. Thedevice of claim 1, wherein each helical fluid channel of the pluralityof helical fluid channels of each first channel layer and each secondchannel layer has a pair of channel walls formed by a pair of helicalwalls of the plurality of helical walls.
 3. The device of claim 1,wherein each helical fluid channel of the plurality of helical fluidchannels of at least one first channel layer and at least one secondchannel layer has a pair of channel walls spaced radially from oneanother and formed by a pair of nested tubular walls of the set ofnested tubular walls.
 4. The device of claim 1, wherein the one or morefirst channel layers and the one or more second channel layers arearranged in a radial series of at least two first channel layersalternating with at least two second channel layers.
 5. The device ofclaim 1, wherein each helical fluid channel of the plurality of helicalfluid channels of each first channel layer and each second channel layeris bounded by a pair of the nested tubular walls and a pair of thehelical walls.
 6. The device of claim 1, wherein the set of nestedtubular walls includes an outermost tubular wall forming at least partof a periphery of the device and at least three nested tubular walls ofsuccessively smaller diameter inside the outermost tubular wall.
 7. Thedevice of claim 1, wherein the set of nested tubular walls, theplurality of helical walls, the first and second intakes, and the firstand second outtakes are formed collectively as a single monolithic unit.8. The device of claim 1, wherein at least one of the first intake andthe second intake includes one or more flow-steering vanes configured toencourage swirling flow of fluid passing through the at least one of thefirst intake and the second intake.
 9. The device of claim 1, furthercomprising a first inflow manifold providing fluid communication betweenthe first intake and each helical fluid channel of the plurality ofhelical fluid channels of each first channel layer, the first inflowmanifold including a plenum and a distribution channel extending fromthe plenum, the plenum being in direct fluid communication with only asubset of the plurality of helical fluid channels of a first channellayer of the one or more first channel layers, the distribution channelproviding fluid communication between the plenum and another subset ofthe plurality of helical fluid channels of the first channel layer ofthe one or more first channel layers.
 10. The device of claim 9, furthercomprising: a second outflow manifold located adjacent the first inflowmanifold and including a plenum, the second outflow manifold providingfluid communication between each helical fluid channel of the pluralityof helical fluid channels of each second channel layer and the secondouttake; and an end cap located at an inlet end of the first channellayer of the one or more first channel layers, the end cap forming awall of the distribution channel of the first inflow manifold andseparating the plenum of the second outflow manifold from thedistribution channel of the first inflow manifold.
 11. The device ofclaim 1, wherein the set of nested tubular walls defines a central axis,and wherein the first intake, the first outtake, the second intake (116,216), and the second outtake define respective axes that are parallel tothe central axis.
 12. The device of claim 1, wherein each helical wallof the plurality of helical walls provides a load path extendingradially and continuously from an outermost tubular wall to an innermosttubular wall of the set of nested tubular walls.
 13. The device of claim1, further comprising a flange projecting from a helical wall of theplurality of helical walls, or from a nested tubular wall of the set ofnested tubular walls, and into a lumen of a helical fluid channel of theplurality of helical fluid channels of a first channel layer or a secondchannel layer.
 14. The device of claim 1, wherein the plurality ofhelical fluid channels of a first channel layer of the one or more firstchannel layers includes a pair of adjacent helical fluid channels havinga pair of channel inlets and a pair of channel outlets, and wherein oneof the helical walls defines an opening that provides fluidcommunication between the pair of adjacent helical fluid channels at aposition intermediate the pair of channel inlets and the pair of channeloutlets.
 15. An aerospace vehicle comprising: a vehicle body; an engineconnected to the vehicle body and configured to power the vehicle bodyin a flight mode; and a heat transfer device connected to the vehiclebody and/or the engine and including a set of nested tubular walls, aplurality of helical walls intersecting each of the nested tubular wallsto form one or more first channel layers nested with one or more secondchannel layers, each first channel layer and each second channel layerincluding a plurality of helical fluid channels, a first intake and afirst outtake in fluid communication with one another via the helicalfluid channels of each first channel layer, for flow of a first fluidthrough the heat transfer device from the first intake to the firstouttake, and a second intake and a second outtake in fluid communicationwith one another via the plurality of helical fluid channels of eachsecond channel layer, for flow of a second fluid through the heattransfer device from the second intake to the second outtake.
 16. Theaerospace vehicle of claim 15, wherein the heat transfer device isconfigured to cool intake air for the engine.
 17. The aerospace vehicleof claim 15, wherein one of the first and second fluids is supercriticalcarbon dioxide.
 18. The aerospace vehicle of claim 17, wherein the heattransfer device is configured to heat the supercritical carbon dioxidefor use as a working fluid in a thermodynamic cycle that converts heatto another form of energy.
 19. The aerospace vehicle of claim 15,wherein the heat transfer device is in fluid communication with aturbine.
 20. A method of transferring heat between fluids using a heattransfer device including a set of nested tubular walls intersected by aplurality of helical walls to form one or more first channel layersnested with one or more second channel layers, the method comprising:passing a first fluid through the heat transfer device between a firstintake and a first outtake via a plurality of helical fluid channels ofeach of the one or more first channel layers of the heat transferdevice; and passing a second fluid through the heat transfer devicebetween a second intake and a second outtake via a plurality of helicalfluid channels of each of the one or more second channel layers of theheat transfer device.